1. Field of the Invention
The present invention relates to position determining techniques which may be used advantageously in optical character recognition systems, and more particularly in such systems which are portable.
2. Description of the Prior Art
The need for and popularity of optical character recognition systems has recently grown enormously due to the tremendous popularity of word processing systems and the like which may employ an optical character reader to input data into the system. In these applications, it has been traditional to employ large mechanical structures for controlling the head that actually scans the characters and converts the optical data into an electrical signal. These automatic scanning structures are able to control the alignment of the sheet being read with the scanning head and also the speed at which the head scans.
The size and complexity of such automatic mechanical scanning structures render them inappropriate for numerous applications in which portability is desirable. To enhance portability, those working in this field have attempted to eliminate the necessity for the large mechanical scanning structure. Thus, U.S. Pat. No. 3,991,299 to Chadima, Jr., et al teaches a bar code scanner in which a pen-shaped instrument is drawn across the bar code in order to read it.
Others have even attempted to develop hand-held readers for codes other than bar codes. Thus, U.S. Pat. No. 4,377,741 to Brekka et al teaches a hand-held optical code reader. However, when advancing from relatively simple bar code readers to more general character scanners, problems arise with respect to alignment of the scanning head with respect to the characters and the speed with which the scanning head proceeds over the characters. Lacking the mechanical structure for controlling these variables, a portable unit must employ alternative solutions to minimize problems associated with alignment or skew and spacing.
U.S. Pat. Nos. 3,918,029 and 3,735,350, both to Lemelson, teach a scanning system which provides a solution to the alignment or skew problem. A guide is provided for directing a scanning element across a row of characters. Thus, prior to scanning, the characters are aligned with the guide. Then, it becomes fairly simple to maintain alignment of the scanning head with the row of characters by sliding the head along the guide. However, even in these patents, codes and not characters are being scanned. A problem may be that although skew errors have been removed, it is still necessary to recognize the scanned characters. If the speed of scanning varies or even is different from a pre-established ideal speed, the proportions of characters that have been read and converted into electrical signals will vary, thus rendering the problem of recognition extremely difficult.
U.S. Pat. No. 3,947,817 to Requa, which teaches a portable, hand-held optical code reader, mentions the problem that variations in scanning speed, producing expansions and contraction of data, render recognition difficult. However, the solution suggested in this patent involves fairly complicated data processing.